Although morphologically similar, as reviewed by D. E. Soltis et al. (2007), diploid and tetraploid Tolmiea each meets the criteria for all of the commonly used species concepts: they are reproductively isolated, so they are biological species; they are distinct evolutionary lineages, so the two cytotypes meet the expectations of the evolutionary species concept; each is monophyletic, so both can be considered phylogenetic (apomorphic) species; they are diagnosable on the basis of chromosome number and molecular characters, thus fitting the phylogenetic/diagnosability species concept; and morphological characters distinguish the two cytotypes (although these may be considered cryptic by some), hence they are taxonomic species.